package exercise.day7;

import java.util.Scanner;

/**
 * @author Dianzhi Han
 * @version 1.0
 * @description: TODO
 * @date 2022/10/31 1:26
 */
public class WY16_Nontwo {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int col = in.nextInt();
        int row = in.nextInt();
        int count = 0;
        int[][] array = new int[row][col];
        for (int i = 0; i < row; i++) {
            for (int j = 0; j < col; j++) {
                if (array[i][j] == 0) {
                    count++;
                    if (i + 2 < row) {
                        array[i + 2][j] = 1;
                    }
                    if (j + 2 < col) {
                        array[i][j + 2] = 1;
                    }
                }
            }
        }
        System.out.println(count);
    }
}
